1. Field of the Invention
The present invention relates generally to electrical converters and, more particularly, but not by way of limitation, to converters suitable for applications having relatively large power requirements.
2. Discussion of the Prior Art
It is known that many power tools and the like, designed for operation from alternating current electrical power, can be operated on direct current supplied, for example, by an automobile alternator operating so as to produce a higher voltage than is normally the case when the alternator is used for usual automotive purposes. Devices are currently on the market which exploit this knowledge by utilizing automobile alternators as the generating means in electrical power generating systems which may, or may not, be mounted on an automobile to utilize the alternator therein. Examples include U.S. Pat. No. 3,845,321, issued Oct. 29, 1974 to Santilli and U.S. Pat. No. 4,074,145, issued Feb. 14, 1978 to Laffoon et al. Such devices have the advantages of ease of transportation to provide electrical power substantially anywhere and the ready availability of repair parts so that a sizable market has grown up in recent years for such devices.
A problem is encountered with regard to a part of this market. In Europe, electrical power supplied by utilities is commonly supplied at 220 volts rather than at the lower voltage common in the United States so that tools designed for European market cannot, in general, be operated from automobile alternator-based power supplies which are currently available. Moreover, a solution to this problem has not been forthcoming via redesigned alternator-based power systems. Two problems militate against such a solution: automobile alternators are designed to produce a considerably lower voltage than the 220 volts required and do not stand up well when used at 220 volts; and a solution along this line would leave unsolved the problem of providing portable electric power capable of being used to operate some tools which operate at 110 volts and others which operate at 220 volts. Accordingly, a need exists for a direct current-to-direct current converter which can be provided as optional equipment to be used with an automobile alternator power system. Moreover, in order that the advantages of the alternator-based system be retained, it is important that the converter be compact, that it be relatively maintenance free, and that it be capable of handling large amounts of electrical power commensurate with the use thereof to operate power tools.
Various types of converters are known to provide relatively high voltage direct current from a relatively low voltage direct current source. One type uses a saturable-core square-wave oscillator such as has been described at Section 182 of "Basic Theory and Application of Transistors" first published by Dover Publications, Inc., New York, New York, in 1963 as a reprint of Technical Manual No. 11-690 published in 1959 by the Department of the Army. An oscillator of this type is particularly desirable for use in a converter designed for the above purpose because the square-wave output of the saturable transformer utilized to achieve oscillation requires that only minimal filtering be utilized after rectification to provide low ripple direct current and, moreover, such oscillators have no moving parts. Thus, it might appear that a converter suitable for use with an alternator-based power generation system could be provided by rectifying and filtering the output of a saturable-core oscillator as has been done in low power applications. In practice, however, such has not proven to be the case. It has been found that a converter cannot be economically constructed in this manner to provide the power output levels required to solve the above problem. The cores of the saturable transformers used in saturable-core oscillators are generally expensive with the cost becoming excessive as larger cores are used. In general, an oscillator core available at a cost commensurate with the above application cannot be used to construct a converter capable of reaching the voltage levels required.